Parent task status should relate to subordinate tasks statuses

When the status of sub ordinate tasks are not completed, i.m.h.o. it should not be possible to put the parent status to completed either. I don't know how it would be most practical to make this relation, but it would be more intuitive and logical to have it.

At the moment all subordinate uncompleted tasks disappear from the hierarchical and with chart view in /node/
/tasks which is logically incorrect and far from intuitive. So I don't know if you can call this a feature request really. May be it is a bug.

May be there should be even more relations?: Cost, time